Intruder in the circuit


The operators of a remotely piloted aircraft (RPA) were lucky to feel only embarrassment rather than grief after their aircraft got lost near a busy aerodrome. It’s an example of why RPA operators must take them seriously as aircraft.

Aviation in itself is not inherently dangerous. But to an even greater degree than the sea, it is terribly unforgiving of any carelessness, incapacity or neglect. So said Captain Alfred Gilmer Lamplugh in 1931, in one of the first attempts to understand the risks of the air.* His words are just as resonant today. They apply even in the almost complete personal safety of operating an unmanned aircraft from a ground station.

In July 2012, an RPA operator, preparing for its unmanned aircraft system (UAS) operator’s certificate application, managed to lose one of its RPA. The RPA ended up in the hands of the Royal Australian Air Force, which was alarmed to discover that it had flown across the final approach path to RAAF Edinburgh. There were training aircraft in the circuit at the time.

The CASA investigator who handled the case takes up the story: ‘this company was looking to get into the UAS industry. The people involved had been involved in aerial photography and decided to start a new company, using RPA.

‘The organisation was looking to get a UAS operator’s certificate and as part of this they decided to do some trial flights. They went to an airfield at Calvin Grove in northern Adelaide, where they had a written agreement with the owner.

‘Unfortunately for them, Calvin Grove happens to be right in the middle of the Edinburgh control zone. That in itself is not necessarily a problem, but there are requirements when you operate in control zones. There is a regulation that says you can only operate in control zones with the permission of the airfield operator and with ATC clearance.

‘On this particular day they chose to conduct their trials without notifying the tower. Their intention was to fly the RPA only within 300 metres of the airfield and below 100 feet above ground level (AGL). No one would have been any the wiser, except that on this particular day they lost control of the RPA. It was last seen spiralling up above 400 feet. It got caught in the prevailing winds and crossed the approach path to RAAF Edinburgh’s runway 18.

‘As in the old saying, what goes up must come down. On this occasion it landed in someone’s backyard. It could have been worse. It could have conflicted with an aircraft on final or in the circuit area. There’s also the issue that it could have come down on top of something, a building, a car, or a person. This time it landed in a backyard and no one was hurt.’

The resident called the Air Force, which was initially alarmed to discover that an RPA equipped with an autopilot, GPS receiver and hi-resolution digital camera had been flying near one of its bases. The potential for snooping, or worse, was obvious. But when the operators placed lost ads in a nearby shopping centre the mystery was solved. Geometrical analysis of the pictures taken by the camera showed the RPA had reached a height of about 1100 feet above ground level. At about the time it was reported lost, a DA42 training aircraft was on an ILS final approach to Edinburgh. It would have been at about 155 feet, nearly 1000 feet lower than the maximum recorded height of the RPA, but the actual separation between the two aircraft could not be determined. It was clearly too close for comfort, and the prospect of about 5 kg of RPA colliding with the windscreen, or one of the engines, of a light twin aircraft flown at low speed and altitude by a low-hours pilot was not to be taken lightly.

The RPA operators, meanwhile, had enlisted the help of the airfield owner to fly a grid search in his aircraft. This was done with all proper permissions and clearances. Indeed, the RPA operators behaved honourably after the incident, despite the prospect of administrative penalties. The inspector found both the controller and the company head ‘polite, cooperative and willing to assist’.

The operator told the CASA investigator: ‘our considered hypothesis is that the most likely cause of the fly-away was internal electrical noise causing the gimbal servos to chatter or move at random. This would cause excessive current demand from the BEC (battery eliminator circuit). The BEC voltage would drop and could cause the R/C (radio control) receiver to brown out’.

If power returned to normal after the R/C receiver was out of range the RPA would have reverted to fail safe mode, holding its control surface positions but shutting off the motor, the operator surmised.

The operator voluntarily made changes to their RPA operation, the main one being to do their testing at another property, near Murray Bridge, far from city, suburbs, airports, or control zones.

The investigator says the story carries a strong safety message for all aircraft operators, manned or otherwise: safety starts before you take off.

‘When you operate a UAV you are flying an aircraft – the fact that you might have bought the airframe from a toy shop is neither here nor there’, he says. ‘You are entering the aviation industry and with that comes increased risk.

‘You are in aviation – the same business as Qantas. You have to consider the risks and dangers of injury to people on the ground, or damage to property on the ground before your aircraft leaves the ground.

‘You need to be aware of those risks and ensure that not only do you comply with requirements – which set the minimum safety standards – but also need to try to minimise the possible consequences of your operations.’

* Lamplugh, a pioneering pilot turned insurance underwriter, was addressing the Royal Aeronautical Society on October 29 1931, giving the first lecture it had ever heard about accident trends. A report can be found in the online archive of Flight International.